How to split a certain area using python?
Iterate through all visible areas and override the context when calling area_split() operator:
import bpy

for area in bpy.context.screen.areas:
    if area.type == 'IMAGE_EDITOR': # 'VIEW_3D', 'CONSOLE', 'INFO' etc. 
        override = bpy.context.copy()
        override['area'] = area
        bpy.ops.screen.area_split(override, direction='VERTICAL', factor=0.3)
        break